adam's suggestion is great too. just get an aluminum frame and race.
aluminum is a great choice too. very stiff...very light. and who cares about the slight comfort benefits of steel/ti/carbon? cx events are short! for the most part...you'll see that most fast racers, semi-pros and pros are riding either aluminum or carbon. only a small percentage ride titanium...same with steel...and probably like no one rides magnesium, wood, or other exotic materials.